The deal was done last night with Rev's signing a 2 and half year deal with the Bluebirds for an undisclosed fee, but its said to be much less than the 400k rumoured fee.
Rev's was out of contract in the summer and this is why Steve Evans has took the decision to sell the clubs top goalscorer in the January window.
"Back last April the football club and the representatives of Alex had been in negotiations to extend the player's contract beyond the summer of 2015. But despite vigorous efforts by both parties sadly an agreement could not be reached." Evans said.
"In a situation such as this any football club must take advantage of any considerable asset and the final offer from Cardiff City met the valuation of our chairman, who has to be said at all times drives a fierce bargain."
"Alex Revell has simply been stunning for Rotherham United and has given me as his manager some wonderful performances, loyalty, commitment and passion."I have spoken to Alex and he knows as a man what my thoughts of him and his young family are. Everyone at Rotherham United is indebted to him and he will be welcome back with open arms at any time in the future."
"He has now joined a fantastic club in Cardiff and he gets the personal rewards that come with such a transfer, we wish him well for the future."he added.